Large-sized and thick compound sleeves of high hardness

ABSTRACT

Large-sized and thick compound sleeves of high hardness adapted for use with back-up rolls of the assembly type having an outer diameter of over 1,000 millimeters and produced by centrifugal casting. Each sleeve comprises an outer layer of high-alloyed cast steel having a shore hardness number in a range between 60 and 75 and a carbon content in a range between 0.4 and 0.9% by weight, and an inner layer of low-alloyed tough cast steel having a shore hardness number in a range between 30 and 45. The sleeves are produced such that the ratio of the thickness of each sleeve to the outer diameter thereof is in a range between 0.10 and 0.30 and the ratio of the thickness of the outer layer thereof to that of the inner layer thereof is in a range between 0.40 and 1.2.

United States Patent 11 1 Maruta et a1.

1 1 LARGE-SIZED AND THICK COMPOUND SLEEVES OF HIGH HARDNESS [75] Inventors: Kenzi Maruta; Atsushi Yamada,

both of Kita-Kyushu; Tsunemi Tsuji, Fukuoka, all ofJapan [73] Assignee: Hitachi Metals, Ltd., Japan [22] Filed: Apr. 30, 1974 [21] Appl. No; 465,587

1 1 July 15, 1975 Primary E.taminerL. Dewayne Rutledge Assistant Examiner-E. L. Weise Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT Large-sized and thick compound sleeves of high hardness adapted for use with back-up rolls of the assembly type having an outer diameter of over 1,000 millimeters and produced by centrifugal casting. Each sleeve comprises an outer layer of high-alloyed cast steel having a shore hardness number in a range between 60 and 75 and a carbon content in a range between 0.4 and 0.9% by weight, and an inner layer of low-alloyed tough cast steel having a shore hardness number in a range between 30 and 45. The sleeves are produced such that the ratio of the thickness of each sleeve to the outer diameter thereof is in a range be tween 0.10 and 0.30 and the ratio of the thickness of the outer layer thereof to that of the inner layer thereof is in a range between 0.40 and 1.2.

3 Claims, 3 Drawing Figures LARGE-SIZED AND THICK COMPOUND SLEEVES OF HIGH HARDNESS This invention relates to compound sleeves adapted for use with back-up rolls of the assembly type having thick rolls fitted on the shafts and used with four-high rolling mills and the like for effecting cold rolling and hot rolling.

Rolls of the assembly type have been widely in use because the shaft portion can be used again and again by replacing one sleeve by another sleeve and rolls of the assembly type are low in roll cost and more economical than rolls of the solid type. It is common practice to use unitary sleeves having a hardness below shore hardness number 60 for use with back-up rolls of the assembly type used with four-high rolling mills and the like for effecting cold rolling and hot rolling. Such sleeves have, however, the disadvantage of being low in resistance to wear and surface roughening.

On the other hand, with the progress of the rolling art and the increase in efficiency in performing rolling, there has in recent years been an increasingly large demand for sleeves having properties as set forth below for use with back-up rolls of the assembly type.

1. The sleeves shoud be tough and devoid of the possibilities of fractures;

2. The sleeves should be highly resistant to wear and should not produce surface roughening;

3. The sleeves should be highly resistant to spalling;

and

4. The sleeves should be highly deep hardening or low in the reduction of internal hardness in the effective use range.

Difficulty has been experienced, however, in producing from a single material large thickness sleeves which meet all the aforementioned requirements. Particularly, it has been impossible to produce such sleeves by casting in a mold because of low strength of the material.

In order to obviate this problem, proposals have been made to produce sleeves of the compound type each comprising outer and inner layers of equal thickness made of dissimilar materials. More specifically, such sleeves would consist of an efi'ective use surface layer or outer layer made of a high-alloyecl material of high hardness which is highly resistant to wear, surface toughening and spalling and which is deep hardening, and an inner layer made of a soft and ductile material of low hardness which is tough and which has a reduced internal residual stress.

Composite sleeves of the prior art have hitherto been produced by casting two types of materials by using a fixed mold provided with a partition of a steel plate, or by first casting a molten metal for the outer layer and replacing the inner portion of the poured molten metal by another molten metal for the inner layer after the outer layer has solidified a predetermined distance from the surface. The former has disadvantages in that the inner and outer layers are sometimes not welded together properly, hot top has little effect because the inner and outer layers are separated by the partition, and degassing of the poured molten metals is not effected properly. The latter has disadvantages in that molten metals for the inner and outer layers tend to be mixed with each other thoroughly, so that it is impossible to perform the operation in a stable manner because difficulty is experienced in controlling the thickness of each layer and the quantity of the molten metal used for each layer. Thus, the aforementioned methods are not in practical use nowadays.

A pipe of small thickness formed in two layers and made of a ferrous or non-ferrous material can readily be produced by centrifugal casting and the two layers form well-defined concentric circular areas because the pipe has a small thickness and the inner and outer layers quickly solidify. Since such pipe is not subjected to a high load both mechanically and thermally in service as is the case with rolls, there is no technical problem to be obviated in producing such pipe.

However, when compound sleeves of large size and thick having a diameter of over 1,000 millimeters and the ratio of the thickness t to the outer diameter D or t/D of over 0.10 are to be produced for use with a rolling mill by centrifugal casting, difficulties are experienced because such sleeves must have the aforementioned properties. The problems which should be obviated in producing such compound sleeves are as follows:

a. It takes a long time for both the inner and outer layers to solidify and variations tend to occur in the rate of solidifying of the molten metals from region to region, thereby making it difficult to provide a compound sleeve with concentric circular layers separated by a boundary layer and each made of a homogeneous material. The inner and outer layers are either mixed too much and no well-defined inner and outer layers are formed, or improper joining by fusion of the inner and outer layers occurs.

b. It is difficult to minimize a residual stress existing in the interior of the boundary layer through which the metals for the inner and outer layers shift from one layer to the other, thereby making it difficult to form a satisfactory boundary layer having no defect throughout the whole sleeve can withstand high rolling stresses.

c. A sleeve in which the thickness of the outer layer and the thickness of the inner layer in cross-section are not proper has the possibilities of failures during production or in service.

d. The rate of solidifying of molten metals is low, and defective segregation tends to occur in the inner and outer layers because of centrifugal casting.

Thus the production of large-sized and large thickness compound sleeves of high hardness by centrifugal casting has been very difficult.

This invention has as its object the provision of ideal composite sleeves for rolls each having predetermined properties, such compound sleeves being produced by centrifugal casting and obviating the aforementioned porblems of the prior art.

According to the invention, there are provided largesized and large thickness sleeves of high hardness produced by centrifugal casting and each having an outer diameter of over 1,000 millimeters, such composite sleeves each comprising an outer layer of high-alloyed cast steel having a Shore hardness number in a range between 60 and and a carbon content in a range between 0.4 and 0.9 by weight, and an inner layer of low-alloyed cast steel having a Shore hardness number in a range between 30 and 45.

According to the invention, there are also provided large-sized and large thickness composite sleeve of high hardness of the type described in which the ratio of the thickness of each sleeve to the outer diameter of the sleeve is in a range between 0.l and 0.30.

According to the invention, there are also provided large-sized and large thickness compound sleeves of high hardness of the type described in which the ratio of the thickness of each sleeve to the outer diameter of the sleeve is in a range between 0.10 and 0.30, and in which the ratio of the thickness of the outer layer of each sleeve to that of the inner layer of the sleeve is in a range between 0.4 and 1.2.

FIG. 1 is a transverse sectional view of a compound sleeve according to this invention;

FIG. 2 is a vertical sectional view of the compound sleeve shown in FIG. 1; and

FIG. 3 is a diagram showing hardness penetration of the compound sleeve.

The invention will now be described with reference to an embodiment shown in FIG. 1 to FIG. 3. FIG. 1 and FIG. 2 show a compound sleeve for back-up roll of the assembly type used for hot strip mills and cold strip mills. The compound sleeve comprises an outer layer of high-alloyed steel of high hardness, an inner layer of tough low-alloyed cast steel of low hardness, and a boundary 3 which is a layer of the mixture of the materials for the two layers. 4 disignates a shrinkage fitting surface.

Large-sized and large thickness compound sleeves of over 1,000 millimeters in diameter for a rolling mill in which the ratio of the thickness 1 to the outer diameter D or MD is in a range between 0.10 and 0.30 are produced as follows. A molten metal for forming the outer layer 1 of high-alloyed steel of high hardness having a Shore hardness number in a range between 60 and 75 and a carbon content in a range between 0.40 and 0.90 is first poured into a mold for centrifugal casting rotating at high speed on a horizontal centrifugal casting machine. Immediately before solidification of the inner surface of the molten metal for the outer layer is completed after solidification has progressed for a predetermined time interval, a molten metal for forming the inner layer 2 of tough cast steel of low hardness having a Shore hardness number in a range between 30 and 45 is poured into the mold in a quantity such that the ratio of the thickness II of the outer layer to the thickness of the inner layer is in a range between 0.4 and 1.2. The outer and inner layers 1 and 2 are mixed and joined by fusion metallurgically perfectly at the boundary 3 and no diffusion of materials, takes place, so that the compound sleeve thus produced is free from flaws as a casting. After the compound sleeve has solidified, rotation of the mold is interrupted, thereby finishing the casting operation. Preferably, a nickel, chrominum or molybdenum alloy steel which increases the handenability and which hardens upon being quenched relatively slowly is employed as the high hardness and highalloyed steel in order to ensure that the outer layer 1 has a Shore hardness number in a range between 60 and 75.

The invention provides large-sized composite sleeves of over 1,000 millimeters in outer diameter. The reason why the ratio t/D is limited to a range between 0.10 and 0.30 is as follows. In the case of small thickness sleeves in which the ratio t/D is below 0.10, cooling and solidifying of the sleeves take place relatively quickly as afore-mentioned, so that there is no problem to be obviated. On the other hand, when the ratio r/D is over 0.30, the thickness of the sleeves is excessively large relative to the diameter, so that it takes a long time for such sleeves to cool and solidify. Thus, it is impossible to produce compound sleeves which meet the predetermined requirements, no matter how the thicknesses of the outer and inner layers are controlled in performing centrifugal casting.

The reason why the Shore hardness number of the outer layer of the sleeves according to the invention is limited to a range between 60 and is as follows. If the Shore hardness number is below 60, then the outer layer is not resistant to wear and spalling; if the Shore hardness number is over 75, then the toughness of the outer layer is markedly reduced, so that cracks are formed when an overload is applied thereto and the surface imperfection renders the sleeves unfit for service.

The reason why the carbon content of the molten metal for the outer layer is limited to a range between 0.4 and 0.9 is as follows. The carbon content should be over 0.4 if the Shore hardness number of the outer layer is to be maintained at a level over 60 and the sleeves can be sufficiently hard to resist wear when the alloy steel used contains nickel, chromium or molybdenum in a percentage such that the alloy steel can be produced economically. If the carbon content exceeds 0.9 then massive carbides take place and the resistance of the sleeves to spalling is lowered. Thus, a high-alloyed nickel, chromium or molybdenum steel having a carbon content in a range between 0.4 and 0.9 is used for the outer layer.

The reason why the ratio of the thickness 1, of the outer layer 1 to the thickness of the inner layer 2 is limited to a range between 0.40 and L2 in the final products is as follows. In order that the boundary 3 may be in a perfect condition for joining the outer layer 1 and the inner layer 2 by fusion, a portion of the inner surface of the outer layer 1 should be melted again by the molten metal for the inner layer 2 and allowed to solidify again. To this end, it is required that the quantity of the molten metal for the inner layer 2 should be such that the ratio t /t is sufficiently high to enalbe the molten metal for the inner layer 2 to have a thermal capacity sufficiently high relative to the volume of the outer layer 1 so that a portion (15 to 20 millimeters in thickness) of the inner surface of the outer layer can be melted again immediately before completion of soldification. Thus, the quantity of the molten metal for the inner layer 2 should be such that the ratio t,/t does not exceed 1.2. If the ratio 1 /1 is below 0.40, then the thickness t of the outer layer l is extremely small as compared with the thickness t, of the inner layer 2. When this is the case, the heat capacity of the molten metal for the inner layer 2 is excessively high relative to the volume of the outer layer 1, with the result that the inner surface of the outer layer 1 is too readily melted again and diffused to enable the outer layer 1 to have a predetermined thickness and to permit the boundary 3 to be formed in the form of a circle free from eccentricity.

If the Shore hardness number of the inner layer 2 exceeds 45, then the inner layer 2 is lowered in toughness and becomes markedly brittle. This increases the hazard of failures of the sleeve during production or in service. If the Shore hardness number of the inner layer 2 is below 30, then the shrinkage fitting surface of the sleeve lacks rigidity, thereby posing the problem of slipping of the sleeve. Thus, the Shore hardness number of the inner layer 2 is limited to a range between 30 and 45 and preferably to a range between 35 and 45. It should be noted that the hardness of the inner layer 2 is closely related to the range 0.40 and 1.2 of ratio t,/t

FIG. 3 shows the depth hardness of a composite sleeve according to the invention. In FIG. 3, a line A represents the depth hardness of a composite sleeve of high hardness accoring to the invention for back-up rolls of the assembly type, and a line B represents the depth hardness of a conventional high hardness sleeve made of a homegeneous material. It will be seen that the outer layer 1 is markedly more deep hardening than the conventional sleeve made of a single material. Thus, even if the sleeve is of the composite type, when the thickness t, of the outer layer having a Shore hardness number in a range between 60 and 75 is such that the ratio t /t exceeds 1.2, the residual tensile stress applied to the inner layer 2 becomes so high that the hazard of fractures is increased.

A compound sleeve produced as aforementioned which meets the aforementioned requirements and in which the boundary between the outer and inner layers is circular in form is worked roughly after being subjected to homogenizing and spherodizing as scheduled. The sleeve is then quenched and tempered and made into a final product in which the ratio t lt is in a range between 0.40 and 1.2. The sleeve is mounted by shrinkage fitting on a shaft prepared beforehand, so that a large-sized and thick composite sleeve of high hardness for a back-up roll is produced.

EXAMPLE Table 1 shows the chemical composition of metals for producing a compound sleeve for a back-up roll in hot strip mills, in which the outer diameter of the sleeve is 1,254 millimeters, the inner diameter thereof is 880 millimeters, the total length is 1,442 millimeters and the outer layer has a thickness of over 70 millimeters.

TABLE 1 of the sleeve was represented by the line A in FIG. 3. The outer layer of the sleeve had an average thickness of 90 millimeters, and the sleeve as a whole had a thickness of 200 millimeters. With a variation in the thickness of the outer layer being within 4 millimeters from region to region, the outer layer was a substantially perfect circle with respect to the outer diameter. The ratio t/D of the sleeve was 0.14, and the ratio t,/t thereof was 0.82, these values being within the predetermined ranges.

Table 2 shows the mechanical properties of the sleeve.

The amount of wear caused on a back-up roll of the assembly type using the aforementioned composite sleeve was 0.55 millimeter for one operation, which was much smaller than an average amount of 1.7 millimeters for conventional rolls. Moreover, the use of the compound sleeve accoring to the invention made it possible to place rolls in service consecutively for 20 days, which is a marked advance on the prior art which enabled the rolls to be placed in service consecutively only for 10 days.

From the foregoing description, it will be appreciated that the present invention provides large-sized and thick compound sleeves of high hardness for back-up rolls of the assembly type in which the material, hardness and thickness of the outer layer can be selected Chemical Composition S Ni Cr Mo 0.005 0.35 5.23 1.10

5,600 kilograms of molten metal for the outer layer kept at a temperature 1560C was poured into a metallic mold rotating at 120 G on a horizontal casting machine for producing large-sized sleeves. After lapse of a predetermined time and immediately before completion of solidification of the inner surface of the outer layer, 4,300 kilograms of a molten metal for the inner layer kept at 1570C was poured in the mold so as to re-melt a portion of the outer layer about 15 millimeters in thickness. Upon completion of solidification of the metals in about four hours, rotation of the mold is stopped. Then, the casting was removed from the mold and worked roughly after being subjected to homogenizing and spherodizing, and hardened in a sleeve quenching and tempering furnace in which temperatures can be controlled with a high degree of precision.

The results of inspections carried out by entire surface coloring and supersonic flaw detecting methods showed that the sleeve was free from flaws. The surface of the sleeve had a Shore hardness in a range between 70 and 71, and the interior of the sleeve had a Shore hardness in a range between 35 and 38. Depth hardness freely to meet the predetermined requirements, and which are of high performance and high solidity with no flaws in the outer layer and the boundary which form concentric circles. The sleeves according to the invention are economical because the molten metals wasted during production are low in quantity. The sleeves are free from fractures in spite of the fact that their hardness is higher than that of conventional sleeves. The sleeves are about twice as long in service life as conventional sleeves and permit rolling to be carried out with a higher degree of efficiency. Since the sleeves are highly hardened and their outer layer show almost no reduction in hardness penetration their performance is not lowered till they are retired from service.

We claim:

1. Large-sized and thick compound sleeves of high hardness produced by centrifugal casting and each having an outer diameter of over 1,000 millimeters, such composite sleeves each comprising an outer layer of high-alloyed cast steel having a Shore hardness number in a range between 60 and and a carbon content in a range between 0.4 and 0.9 by weight, and an inner layer of low-alloyed cast steel having a Shore hardness number in a range between 30 and 45.

2. Large-sized and thick composite sleeves of high hardness produced by centrifugal casting and each having an outer diameter of over 1,000 millimeters, such compound sleeves each comprising an outer layer of high-alloyed cast steel having a Shore hardness number in a range between 60 and 75 and a carbon content in a range between 0.4 and 0.9 by weight. and an inner layer of low-alloyed cast steel having a Shore hardness number in a range between 30 and 45, the ratio of the thickness of each sleeve to the outer diameter of the sleeve being in a range between 0.10 and 0.30.

3. Large-sized and thick compound sleeves of high hardness produced by centrifugal casting and each having an outer diameter of over 1,000 millimeters, such compound sleeves each comprising an outer layer of high-alloyed cast steel having a Shore hardness number in a range between 60 and and a carbon content in a range between 0.4 and 0.9 by weight, and an inner layer of low-alloyed cast steel having a Shore hardness number in a range between 30 and 45, the ratio of the thickness of each sleeve to the outer diameter of the sleeve being in a range between 0.10 and 0.30, the ratio of the thickness of the outer layer to that of the inner layer being in a range between 0.40 and L2. 

1. LARGE-SIZED AND THICK COMPOUND SLEEVES OF HIGH HARDNESS PRODUCED BY CENTRIFUGAL CASTING AND EACH HAVING AN OUTER DIAMETER OF OVER 1,000 MILLIMETERS, SUCH COMPOSITE SLEEVES EACH COMPRISING AN OUTER LAYER OF HIGH-ALLOYED CAST STEEL HAVING A SHORE HARDNESS NUMBER IN A RANGE BETWEEN 60 AND 75 AND A CARBON CONTENT IN A RANGE BETWEEN 0.4 AND 0.9 % BY WEIGHT, AND AN INNER LAYER OF LOW-ALLOYED CAST STEEL HAVING A SHORE HARDNESS NUMBER IN A RANGE BETWEEN 30 AND
 45. 2. Large-sized and thick composite sleeves of high hardness produced by centrifugal casting and each having an outer diameter of over 1,000 millimeters, such compound sleeves each comprising an outer layer of high-alloyed cast steel having a Shore hardness number in a range between 60 and 75 and a carbon content in a range between 0.4 and 0.9 % by weight, and an inner layer of low-alloyed cast steel having a Shore hardness number in a range between 30 and 45, the ratio of the thickness of each sleeve to the outer diameter of the sleeve being in a range between 0.10 and 0.30.
 3. Large-sized and thick compound sleeves of high hardness produced by centrifugal casting and each having an outer diameter of over 1,000 millimeters, such compound sleeves each comprising an outer layer of high-alloyed cast steel having a Shore hardness number in a range between 60 and 75 and a carbon content in a range between 0.4 and 0.9 % by weight, and an inner layer of low-alloyed cast steel having a Shore hardness number in a range between 30 and 45, the ratio of the thickness of each sleeve to the outer diameter of the sleeve being in a range between 0.10 and 0.30, the ratio of the thickness of the outer layer to that of the inner layer being in a range between 0.40 and 1.2. 